This invention relates to optical fiber cable, and in particular to constructions of such cables that are gas blocking.
In view of their potential for use in a submarine environment cable constructions have been proposed that are held out to be water blocking so that should such a cable be cut when submerged the penetration of water shall be limited. One example of a patent specification directed to water-blocked optical fiber cable is given by United Kingdom Patent Specification No. 2099179A. Although there are some similarities between the factors necessary to achieve satisfactory gas blocking, there are also major differences which are attributable in part to the much lower viscosity of gases, to the smaller values of hydrostatic pressure typically to be resisted, and to the fact that in achieving a gas-blocking design due attention must be paid to the prevention of ballooning of the cable sheath. It is in consideration of this last mentioned factor that the present invention is particularly concerned with cable constructions employing relatively high tensile modulus sheath materials.